Interpretive Summary: The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. It causes approximately $6 billion in damage annually in livestock and agricultural production and poses a serious threat to human health. USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (CMAVE, Gainesville, FL) have recently discovered a new RNA virus in the fire ant. Studies suggest that the virus (SINV-2) may be a potential microbial control agent for fire ants. In order to develop the virus as a control agent for fire ants, a more thorough understanding of the virus is necessary. To accomplish this goal, scientists CMAVE successfully determined the ant stage and cell type infected and a method to transmit the virus to uninfected ants. These tests will help development of SINV2 as a possible microbial insecticide against fire ants.

Technical Abstract:
Solenopsis invicta virus-2 (SINV-2) is the second virus identified from the fire ant, Solenopsis invicta, Buren. SINV-2 is unique among positive—strand RNA viruses from insects by possessing four cistrons in a monopartite genome. Fire ant colonies testing positive for SINV-2 by RT-PCR did not exhibit any discernable symptoms. RT-PCR-based surveys for SINV-2 among 688 fire ant mounds in Alachua County, Florida, sampled during the period January 2006 through December 2007 showed that the prevalence of SINV-2 among nests ranged from 1.6 to 16.4 %. Unlike Solenopsis invicta virus-1, no seasonal-associated prevalence was observed with regard to SINV-2 infection among fire ant colonies. No social form-specificity was evident; SINV-2 was found in both monogyne and polygyne S. invicta nests. Real-time quantitative PCR experiments showed that SINV-2 genome equivalents per individual ant ranged from 1.9 x 107 in pupae to 4.3 x 1011 in inseminated queens. The SINV-2 infection was detected in all ant stages examined (eggs, larvae, pupae, workers, and queens). Tissue tropism studies indicated that the alimentary canal (specifically the midgut) is most likely the susceptible tissue. SINV-2 was successfully transmitted to uninfected S. invicta ants by feeding a partially purified homogenate of SINV-2-infected ants. The SINV-2 transmission rate ranged from 30-80%, and both positive (genomic) and negative (replicative) SINV-2 RNA strands accumulated in recipient ants over the course of the experiment. These results indicated that SINV-2 replicates within S. invicta.